Determine if NSUInteger has a value or is nil

Question

I'm trying to use a HKAnchoredObjectQuery on iOS.

To do so I have to provide an anchor to the query which in this case is a NSUInteger. I want to save this integer for queries in the future in the NSUserDefaults and just simply want to use

if(anchor != nil) { // do stuff }

But the complier tells me that I'm not allowed to do this because I'm comparing a integer to a pointer and I understand why I'm not able to do this but I don't know how to do it.

The error code is this

Comparison between pointer and integer ('NSUInteger' (aka 'unsigned long') and 'void *')

Does anyone know how I'm able to determine if my anchor has a value or not?

Use this as anchor is NSUInteger , so if(anchor != 0) { //do stuff } — Paresh Navadiya, Apr 13 '15 at 12:43
Use a NSNumber to hold the integer which you can compare against nil. If the object is not in UserDefaults then it is not set. Otherwise it has the value inside the NSNumber. — Rory McKinnel, Apr 13 '15 at 13:35

score 2 · Accepted Answer · answered Apr 13 '15 at 12:47

2

NSUInteger is a primitive type, not an object type. NSNumber is an object type. For an NSNumber object, you can check whether it is nil or not. An NSUInteger is never nil because it is an integer, not a pointer.

Many functions that return NSUInteger as a result for a search return the constant NSNotFound if the search failed. NSNotFound is defined as a very large integer (2^31 - 1 for 32 bit, 2^63 - 1) for 64 bit).

answered Apr 13 '15 at 12:47

gnasher729

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Pro tip: `NSNotFound` is a negation so you have to make your statement true otherwise it will just skip over your `if` statement. – Constantin Jacob Apr 14 '15 at 08:40

score 0 · Answer 2 · answered Apr 13 '15 at 12:47

NSUInteger is not an object and cannot be compared to nil. In over-simplistic terms, an object is a pointer to a memory location that may contain an value or be nil. NSUInteger is just a value. It may be 0, or some other value that you don't expect, but it will have a value.

score 0 · Answer 3 · answered Apr 13 '15 at 12:47

An NSUInteger cannot be nil because it is not an object. The default value on creation would be zero. To save in NSUserDefaults, you could store it as an NSNumber, which could be checked for nil later.

To store it in NSUserDefaults:

NSNumber *aNumber = @(anchor);
[[NSUserDefaults standardUserDefaults] setObject:aNumber forKey:aKey];

To get the anchor back from NSUserDefaults:

NSNumber *aNumber = [[NSUserDefaults standardUserDefaults] objectForKey:aKey];
if (aNumber != nil) {
    NSUInteger anchor = [aNumber integerValue];
}

score 0 · Answer 4 · answered Apr 13 '15 at 12:51

NSUInteger or simply int are basically primitive data types and they should be compared with the integer values with in the range of the corresponding data types. nil is used with referenced objects.

In your case, as anchor is NSUInteger so you should use integer value for comparison in place of nil as-

if(anchor != 0) {
// do stuff
}

Determine if NSUInteger has a value or is nil

4 Answers4